I own both iphone 5 black (yellow screen) and iPod 5th generation silver (cool screen). To me, yellow screen is easier to read and clearer compared to the cool screen. Just my 2 cents.
I did a survey also. I discover that most of the iphone white has cool screen while Black iphone has yellow screen. I think the reason is to compensate the contrast it creates from the black front. Any thoughts?
Other way around for me. Dad has a perfect blue black iPhone 5 and I've gone through 3 white iPhones and they have all been yellow. This is actually making me want to go back to black... but who knows. :/